QoL improvements to GrTAllocator

-Adds main comment
-Simplify constructor
-Avoid running trivial destructors (maybe compilers would know to remove the entire loop, but this helps make that clearer).

Change-Id: I3825ef21c0d74933df54ca4f532492e5c997f0e9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/302642
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
1 file changed